Fiberglass insulation with binder that is insufficiently cured exhibits poor performance. Cure of phenolic resin is traditionally inspected through a change in color of the resin after (oven) curing. On non-dyed fiberglass products, the product changes from white to yellow after curing at the appropriate operating conditions. However, some binders are dyed black, which does not allow for visual inspection of the binder cure. Therefore, it would be desirable to provide a method of determining the degree of cure of products that include a phenolic binder.